I'll be interested to hear what other people have to say - I imagine it's pretty common knowlege. Purely from a 'physics' point of view, I think additional weight would have more effect on acceleration/climbing than max speed on the flat/downhill.

That website has some heroic assumptions around frontal area, road surface and so on, and thus can't be relied upon for power estimates. But putting in a 4 km hill at 4%, playing with only the weight of the bike and keeping everything else the same, gives me ~1 second per km per kg or less. There appears to be a bug on the site so it doesn't vary at all for a 1 kg change. But if you take the weight variance up to 6 or 10 kg, the pattern emerges.

A 1 kg drop in body weight can often be associated with improving fitness. To take out fitness as a factor, the relevant calculation should be the impact of adding a full bidon to your set up - which is pretty close to 1 kg.

The full impact of weight loss depends on you individually. My normal weight fluctuates through a 3 kg range of 79 kg to 82 kg, but find I actually climb best at the top of that range.

Keep in mind that a change of mass has very little impact on air resistance, which is the dominant resistance force on flatter terrain. Some lighter bikes might indeed have a worse aerodynamic set up and be slower.

As the road tilts up beyond 4%, you will gain speed roughly in proportion to the overall change in mass, multiplied by the factor in orange in the chart below.

e.g. if you drop total system mass by 5%, then your speed gain (for same power output) on a +10% gradient will be ~ 5% x 90% = 4.5%.

on any road; the mass of the bike and rider will ONLY impact on acceleration. On a flat road this means increasing the mass will slow down the rate of change of speed up to the maximum your legs will allow (due to wind resistance, not mass). On a hilly road, each change upwards will mean that you will also be moving that mass upwards, which requires more energy, not necessarily more power (more power if done in same time) PE = m.g.h

generally, whenever the bike/rider is accelerating there is a need for a NET force (speeding up, slowing down, changing direction), this net force needs to be increased when the mass increases (Newton's 2nd Law) If the bike/rider is not accelerating there is no need for an increase in effort. i.e. a heavy bike will be no slower than a light one; it's only the time it takes to reach that top speed that is different.

I'm more inclined to think that the rider will always make more of a difference than the bike.

Just take the TDF as an example.They're all riding great bikes and are all elite cyclists however some can break away, some can stay with the front of the peloton, some at the back and some can't keep up.It's not the bike holding them back, it's the rider.

Dropping your bike's weight from 12kg to 9kg would make a difference but I don't think it would make a noticeable difference to your ave speed (on the flat).You would likely find acceleration and handling is improved but once you're "up and rolling along" you still have to fight against the air resistance and the faster you go the more resistance you fight against. If you're not fit/strong enough to maintain the fight your average speed will drop.

I think improving your fitness, so you are stronger to fight against that air resistance along with your honing your riding technique will make a much bigger difference to your ave speed....along with helping your cycling overall.

I don't blame the bike at all , in fact I love it! Just looking for ways to save energy and/or increase speed, just like a truck uses less petrol if it carries no load.

The plan is to be able to climb moderate hills around 6-7% in a comfortable manner (read faster) by Nov-Dec.This comes after my lungs nearly exploded on the way up a few months ago when I didn't know the importance of warming up or cadence...

Longer term plan is joining a club and enjoying 100km+ rides around hilly Melbourne not gasping for air like I normally do

Cadel wrote:I don't blame the bike at all , in fact I love it! Just looking for ways to save energy and/or increase speed, just like a truck uses less petrol if it carries no load.

The plan is to be able to climb moderate hills around 6-7% in a comfortable manner (read faster) by Nov-Dec.This comes after my lungs nearly exploded on the way up a few months ago when I didn't know the importance of warming up or cadence...

Longer term plan is joining a club and enjoying 100km+ rides around hilly Melbourne not gasping for air like I normally do

Well, I hope that everyone's comments have helped.

It's been pointed out that, for instance, a 3kg lighter frame won't make you faster on the flat, but perhaps 3% faster up hills.

A UK doctor a couple of years ago kept meticulous records of alternating a long fast commute each day between a carbon and a steel bike, and published the results in Lancet, IIRC. Nothing between them.

But even for the different circumstances of climbing, he would suggest the best result would be the rider to lose 3kg of weight by November/December.

clackers wrote:A UK doctor a couple of years ago kept meticulous records of alternating a long fast commute each day between a carbon and a steel bike, and published the results in Lancet, IIRC. Nothing between them.

And it was a pretty ordinary piece of science writing too. I sure hope the same Doc doesn't do medical research.

PawPaw wrote:Add 3kg in the form of 2x 1 litre water bottles to your bidons, and strap another to your top tube. Then see if you can sustain the same average speed over 20 minutes, for roughly the same heart rate.

There is so much slop in HR response that any speed difference would be less than the noise associated with such a variable.

PawPaw wrote:What would even be more accurate is to use a power meter before and after, and hold the watts at the same level for both intervals, and see what difference you get in average speed.

In order for it to be accurate, you will need to know, precisely, the environmental conditions in order to do such an analysis.

Even a minor change in wind undetectable to a human would be enough to mask such results.

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